The present invention relates generally to intumescent flame retardant polymers and more specifically to intumescent compositions including a matrix polymer, an intumescent composition including an acid catalyst component, a nitrogen source and an ionic phyllosilicate synergist.
Flame retardant polymer compositions are well-known in the art. Because of potential environmental and toxicity concerns, there is increasing interest in antimony and halogen-free systems which provide the desired flame retardant properties to a polymeric article. Phosphorous-based compositions are shown, for example, in Publication Nos. WO 99/43747 and WO 97/41173.
The ""747 publication entitled Flame Retardant Polymer Blends discloses an antimony-free combination of a phosphate-based flame retardant, especially an aryl diphosphate, and an organoclay which are reported to afford synergistic flame retardant properties to polymer blends, especially polyphenylene ether-polystyrene blends and blends of polycarbonates with styrene copolymers such as ABS copolymers. The polyphenylene ether-polystyrene blends free from fluorocarbon additives are preferred according to the disclosure.
The ""173 publication entitled Flame Retardant Composition for Polymers claims a flame retardant composition, adapted to be mixed with a polymer substrate to confer flame retardancy on the substrate, which comprises: (a) a bicyclic phosphorus flame retardant compound, such as one containing one or more pentaerythritol phosphate alcohol moieties, as exemplified by bis(pentaerythritol) phosphate alcohol carbonate; (b) an intumescent flame retardant compound containing nitrogen and phosphorus, such as melamine phosphate; and (c) a monophosphate ester compound to enhance the charring and processing characteristics of the composition in the polymer substrate, such as a liquid aryl group containing phosphate ester compound. The monophosphate ester compound is typically triphenyl phosphate.
See, also, U.S. Pat. No. 4,454,064 to Halpern et al. which discloses a method for the preparation of pentaerythritol phosphate by mixing pentaerythritol and phosphorous oxychloride in a solvent and heating to a temperature of 75 to 125xc2x0 C., as well as U.S. Pat. No. 5,237,085 to Telschaw et al. which teaches synthesis of pentaerythritol-based phosphorous heterocycles by reaction of a pentaerythritol polyol with either a trivalent or pentavalent compound using an aryl phosphate solvent at an elevated temperature. A variety of bicyclic phosphate compounds are likewise disclosed in U.S. Pat. No. 3,293,327 to Hechenbleikner et al.
Intumescent flame retardant compositions including 2,6,7-trioxa-1-phosphobicyclo[2.2.2.]octane-4-methanol-1-oxide and a nitrogen compound selected from the group melamine, ammeline, benzoguanidine, guanidine, urea and salts thereof, are reported to be intumescent and readily adapted to flame retard a variety of dissimilar resins including polyolefins, polyvinylaromatic resins, polycarbonates, polyacrylates, polyamides, PVC and blends thereof in U.S. Pat. No. 4,341,694 to Halpern.
U.S. Pat. No. 5,204,393 to Nalepa et al. describes a flame retardant intumescent polyolefin which comprises a combination of ammonium polyphosphate, tris(2-hydroxyethyl) isocyanurate; melamine cyanurate; and a selected silica in an amount from 0.5 percent to an amount equal to one-half the amount by weight of tris(2-hydroxyethyl) isocyanurate.
Intumescent polymer systems generally are believed to function by way of (1) a carbonific or char-forming component which can be the polymer itself, (2) an acid generating component which acts as a catalyst and (3) a spumific or blowing agent, typically a nitrogen source of both ammonia and N2. The greater the char volume, the better the insulating, whereas the inner cross-sectional core should be cellular and close celled. In addition, the surface crust should be thick, continuous and impenetrable. See Scharf, D. J., Intumescent Fire Retardants for Plasticsxe2x80x94A Continuance (undated). The catalyst or acid generating component is frequently a phosphorous derivative, the function of which is to catalyze dehydration. See Lewin, M., Some Aspects of Synergism and Catalysis in FR of Polymeric Materialsxe2x80x94An Overview, Ninth Annual BCC Conference on Flame Retardancy, Business Communications Co., Inc. Norwalk Conn., wherein ammonium polyphosphate is described as the acid generating component and nitrogen source in a polypropylene system where the polymer itself is the carbonific or char-forming agent.
Perhaps more typically, an organic polyol is used as a carbonific and melamine or a melamine derivative as a spumific. See Scharf, D. et al, Studies on Flame Retardant Intumescent Char: Part I, Fire Safety Journal 19, pp. 103-117, Elsevier (Ireland, 1992). In this publication, it is reported that titanium dioxide in suitable amounts exerts a reinforcing or synergistic flame retardant effect, whereas stannous oxide is antagonistic. Likewise, it has been reported that zinc and manganese salts can benefit APP performance. See Lewin et al., Mn and Zn Compounds as Catalysts of Intumescent Flame Retardancy of Polypropylene, May, 2000, BCC Conference.
In any polymer system, it is desirable to limit or minimize expensive additives from a cost perspective. In addition, additives can have adverse effects on processing or properties which, of course, becomes more pronounced as the additive load in the system increases. The commercial success of intumescent polymer systems has clearly been limited by the high loading of acid generating component and spumific required to achieve the desired (typically 94V-O) rating in terms of flame resistance.
It has been found in accordance with the present invention that certain ionic phyllosilicates, particularly montmorillonoid layered silicates exert a synergistic effect in intumescent polymer compositions making it possible to lower the amount of additives required for a given level of flame resistance, for instance, to maintain a V-O rating under UL-94 standards utilizing otherwise known acid and nitrogen sources. There is thus provided in accordance with a first aspect of the present invention an intumescent, polymer composition including: a matrix polymer composition; an acid catalyst source; a nitrogen source; and an ionic phyllosilicate in an amount of from about 0.1 to about 2 weight percent of the composition, the ionic phyllosilicate having a cationic exchange capacity of at least about 5 meq per 100 g thereof and being capable of synergizing the intumescence of the composition.
In a particularly preferred class of compositions there is provided an intumescent polypropylene composition including: polypropylene; a cyclic organophosphorous acid catalyst source; a nitrogen source selected from the group consisting of amines, ureas, guanidines, guanamines, s-triazines, amino acids, salts thereof including phosphate, phosphonate, phosphinate, borate, cyanurate and sulfate salts, as well as mixtures of the foregoing; and a montmorillonoid ionic phyllosilicate in which the ionic phyllosilicate is present in an amount of from about 0.1 to about 2 weight percent.
In another aspect of the present invention there is provided a flame retardant additive composition for dispersing in a matrix polymer composition to promote intumescence including: an acid catalyst source; a nitrogen source; an ionic phyllosilicate having a cationic exchange capacity of at least about 5 meq per 100 g thereof; and optionally an organic polyol as a carbonific char-promoting agent, wherein the ionic phyllosilicate is present in an amount of from about 0.5 to about 10 percent by weight of the composition.
The invention is described in detail below with reference to numerous exemplary, illustrative and preferred embodiments thereof for purposes of description only. Modification to such embodiments within the spirit and scope of the invention, set forth in the appended claims, will be readily apparent to one of skill in the art. It will further be appreciated that the components of the invention undergo chemical interaction to form other materials, particularly during combustion. Therefore, the invention is directed to the inventive compositions whether or not any chemical interaction has taken place; that is, the invention includes both compositions comprising the recited compositions, as well as reaction products thereof.
The inventive compositions typically include a matrix polymer, an acid source, a carbonific and spumific or nitrogen source component. These components may be in the same chemical compound. For example, ammonium polyphosphate will function as both an acid source and a nitrogen source as will be readily appreciated by one of skill in the art. Likewise, pentaerythritol phosphate alcohol (PEPA) functions as both an acid source and a carbonific. Melamine phosphate can provide carbon for the char, nitrogen for foaming and acid to catalyze dehydration and thus is a particularly preferred ingredient.
In some embodiments, the acid source and nitrogen source are supplied in whole or in part by way of a single chemical compound selected from the group consisting of: ammonium phosphate, ammonium polyphosphate, ammonium pyrophosphate and mixtures thereof.
Intumescent polymer compositions are those that foam and char to provide flame resistance, typically increasing in volume by more than 50 percent, preferably on the order of 100 percent based on the unreacted volume of the composition. The compositions thus typically include an acid catalyst source, a nitrogen source and a carbonific which may be the matrix polymer itself or may be a polyol, or may be provided by way of a multifunctional ingredient such as pentaerythritol phosphate alcohol. The ionic phyllosilicates operate to minimize the amount of additive, be it acid or nitrogen source required to impart a 94V-O rating to the composition. Typically, the ionic phyllosilicate will be operative to reduce the amount of acid, nitrogen and carbonific additives so required by at least about 10% and preferably at least 20% based on the weight of additive.
Acid sources may be borates, sulfates, sulfites, nitrates, phosphates, phosphonates, melamine or other salts of the foregoing, and so forth. Exemplary materials include alkyl diphenyl phosphates; trimethyl phosphate, (C3H9O4P); triphenylphosphine oxide, (C18H15OP); triphenyl phosphate, (C18H15O4P); ammonium phosphates, such as monoammonium phosphate, (NH4H2PO4) and diammonium phosphate, (NH4)2HPO4; ammonium polyphosphate (NH4PO3)n; amine phosphates, such as melamine phosphates, e.g., melamine orthophosphate (C3H6N6 H3O4P); dimelamine orthophosphate (2C3H6N6 H3O4P); melamine pyrophosphate (2C3H6N6 H4O2P2), and the like; trialkyl phosphates, such as triethyl phosphate (C6H15O4P) or trioctyl phosphate, (C24H51O4P); dimethyl methylphosphonate, (C3H9O3P); and diethyl ethylphosphonate, (C6H15O3P); halogenated alkyl phosphates and phosphonates, such as tris(2-chloroethyl) phosphate, (C6H12Cl3O4P); tris(1-chloro-2-propyl) phosphate, (C9H18Cl3O4P); tris(1,3-dichloro-2 propyl) phosphate, (C9H15Cl6O4P); tris[3-bromo-2,2-bis(bromomethyl)propyl] phosphate (C15H24Br9O4P); and bis(2-chloroethyl)-2-chloroethyl phosphonate; diphosphates, such as 2-chloroethyl diphosphates, e.g., tetrakis(2-chloroethyl); ethylene oxyethylene diphosphate, (C12H24C4O9P2); C13H24Cl6O8P2 (Albright and Wilson""s Antiblaze 100); 2-chloroethyl 2-bromoethyl 3-bromoneopental phosphate, (C9H18Br2ClO4P) from Great Lakes Chemical Corporationxe2x80x94Firemaster 836; cyclic phosphonates, such as C15H31O9P3 (Albright and Wilsons"" Antiblaze 19 and 1045); cyclic neopentyl thiophosphoric anhydride; aryl phosphates, such as cresyl diphenyl phosphate, (C19H17O4P); triaryl phosphates, such as triphenyl phosphate, (C18H15O4P); tetraphenyl resorcinol diphosphate, (C38H24O8P); tris(2,4-dibromophenyl) phosphate, (C18H9Br6O4P); diphosphine oxides, such as Cyagard RF1204 from American Cyanamid.
Bicyclic organophosphorous compounds useful as an acid catalyst source within the instant invention are pentaerythritol phosphite, trimethylolpropane phosphite, trimethylolethane phosphite, trimethylolbutane phosphite, trimethylol isobutene phosphite, trimethylol pentane phosphite, trimethylolhexane phosphite, trimethylolheptane phosphite, trimethylol octane phosphite, trimethylolnonane phosphite, trimethylolundecane phosphite, trimethylolheptadecane phosphite, pentaerythritol phosphate, pentaerythritol thiophosphate, pentaerythritol selenophosphate, trimethylolpropane phosphate, trimethylolpropane thiophosphate, trimethylol propane selenophosphate, trimethylolethane phosphate, trimethylolethane thiophosphate, trimethylolethane selenophosphate, trimethylolbutane phosphate, trimethylol butane thiophosphate, trimethylolpentane phosphate, trimethylolpentane thiophosphate, trimethylolpentane selenophosphate, trimethylolhexane phosphate, trimethylolhexane thiophosphate, trimethylolheptane phosphate, trimethylolheptane thiophosphate, trimethyloloctane phosphate, trimethyloloctane thiophosphate, trimethylolnonane phosphate, trimethylolnonane thiophosphate, trimethylolnonane selenophosphate, trimethyloldecane phosphate, trimethyloldecane thiophosphate, trimethylolundecane phosphate, trimethylolundecane thiophosphate, trimethylolheptadecane phosphate, trimethylolheptadecane thiophosphate and trimethylolheptadecane selenophosphate.
Particularly preferred is pentaerythritol phosphate alcohol, which is sometimes referred to simply as pentaerythritol phosphate and which has the following general structure: 
Derivatives of the bicyclic phosphorus compounds may also be used. For example, esters, ethers and carbonates of pentaerythritol phosphate alcohol are known flame retardant components of intumescent systems.
Additional examples of intumescent phosphorus-containing flame retardants include melamine salts of organophosphates such as melamine phenyl phosphate and melamine amyl phosphate.
In accordance with the present invention, a combination of an ionic phyllosilicate, an acid catalyst source, a nitrogen source, and optionally a char-promoting species are processed into a resin to provide a resin composition or product that has improved flame retardant properties and/or lower overall cost. If the flame retardant exhibits sufficient intumescent behavior, then the flame retardant material can be used with the ionic phyllosilicate without the use of a separate char-promoting compound to provide an additive system for flame retardant applications in resins. However, if so desired char-promoting additives can be useful and include polyhydridic alcohols such as pentaerythritol, dipentaerythritol, tripentaerythritol, inositol, adonitol, dulcitol, and 1,3,5-tris(2-hydroxyethyl)cyanuric acid, as well as pentate salts of amino-s-triazines, as disclosed in Fleenor, Jr. U.S. Pat. No. 4,253,972 hereby incorporated by reference. Examples of polymeric char-promoting additives include novolac resins, polyphenylene oxides and polycarbonates. When char-promoting additives are included with the phosphorus-containing flame retardant additive, then should be added in an amount of about 1% to about 10% by weight, based on the weight of the polymer being flame retarded.
Compounds useful as nitrogen sources include any suitable compounds which generate N2 and optionally ammonia such as amines, ureas, guanidines, guanamines, s-triazines, amino acids, and salts thereof including phosphate, phosphonate, phosphinate, borate, cyanurate and sulfate salts. Some specific examples are melamine, urea, benzoguanamine, ammeline, guanidine, cyanoguanidine and glycine; melamine phosphate, melamine pyrophosphate and melamine polyphosphate; ammonium phosphate, ammonium pyrophosphate and ammonium polyphosphate, ethylenediamine phosphate, melamine or ammonium cyanurate and melamine or ammonium borate. Most preferred are melamine phosphate and ammonium polyphosphate.
The characteristics and classification of layered silicates are discussed at length in An Introduction to Clay Colloid Chemistry, H. Van Olphen, Ed., Ch. 5, pp. 57-77, the disclosure of which is incorporated herein by reference. In general, clays are phyllosilicates having two-dimensional arrays of silicon-oxygen tetrahedral and two-dimensional arrays of aluminum- or magnesium-oxygen-hydroxyl octahedral. Of particular interest to the present invention are the layered silicates of ionic character, that is, where the silicates are characterized by a substantial cation exchange capacity, at least about 5 milliequivalents (meq) per 100 grams of clay, termed ionic phyllosilicates or layered ionosilicates herein, as opposed to substantially neutral layered silicates such as talc or kaolinites with less than about 5 meq of cation exchange capacity per 100 grams of material. Particularly preferred are such layered silicates wherein the cation exchange capacity of the layered silicate is more than about 25 meq of cation exchange capacity per 100 grams of silicate. Most preferred are those layered silicates of the smectite class, also referred to in the art as montmorillonoid clays which typically have cation exchange capacities of about 70 meq or more per 100 grams of material. Clays useful in accordance with the present invention may have cation exchange capacities of up to about 150 meq per 100 grams of material. Montmorillonoid silicates are further characterized in that they undergo reversible expansion on absorbing water and have a characteristic structure in which water molecules are situated between sheets composed of two layers of silicon atoms sandwiching one nominally of aluminum and/or magnesium, the silicon and aluminum/magnesium being variously replaced by other elements as hereinafter described. It is believed that layered ionic phyllosilicates with low iron content are especially preferred since iron may have an antagonistic effect on intumescent performance of the system. Preferred ionic phyllosilicates are those having less than about 3 percent by weight of iron, with less than about 1 percent by weight being most preferred Especially preferred montmorillonoids for use in connection with the invention include sodium montmorillonite clay and sodium hectorite clay (aluminum and/or magnesium containing silicates) as further discussed herein.
Inorganic cation (alkali metal, for example) or organic-reacted (organophilic) smectite clays, such as montmorillonite clays or any other clay having an aspect ratio of at least 40, preferably at least 50, more preferably at least 75, are generally those employed in connection with the present invention. Examples of suitable clays include phyllosilicates, such as smectite clay minerals, e.g., montmorillonite, particularly sodium montmorillonite; magnesium montmorillonite and/or calcium montmorillonite; nontronite; beidellite; volkonskoite; hectorite; laponite; saponite; sauconite; vermiculite; and the like. Other useful layered materials include illites, such as micaceous minerals and mixed layered illite/smectite minerals, which are optionally made organophilic by reaction or ion-exchange.
Suitable organic cations intercalated via ion-exchange into the interlayer spaces between adjacent layered material platelets may be primary, secondary, tertiary or quaternary onium ions having Formula I or Formula II, as follows: 
wherein Xxe2x95x90P or N, and wherein Yxe2x95x90S or O; and
wherein R1, R2, R3 and R4, same or different, are H, or organic moieties, such as linear or branched alkyl, aryl or aralkyl moieties having 1 to 24 carbon atoms.
The more preferred onium ions are quaternary ammonium ions having Formula I, wherein R1, R2, R3 and R4 are moieties, same or different, selected from the group consisting of H, alkyl, benzyl, substituted benzyl, e.g., straight or branched chain alkyl-substituted and halogen-substituted; ethoxylated or propoxylated alkyl; ethoxylated or propoxylated benzyl, e.g., 1-10 moles of ethoxylation or 1-10 moles of propoxylation.
Among the preferred silicate layered materials are phyllosilicates of the 2:1 type having a negative charge on the layers ranging from about 0.018 to about 0.36 charges per formula unit and up to about 0.55 charges per formula unit and a commensurate number of exchangeable metal cations in the interlayer spaces. As noted above, most preferred are layered materials are smectite (montmorillonoid) type of clay minerals such as montmorillonite, nontronite, beidellite, volkonskoite, hectorite and saponite. The preferred clay materials generally include interlayer cations such as Na+, Ca+2, K+, Mg+2, NH4+ and the like, including mixtures thereof.
The amount of organic cation compound which can be used if so desired, such as onium ion or protonated amine, reacted or ion-exchanged with the layered silicate materials, may vary substantially between about 2%, preferably at least about 10%, and about 200%, based on the dry weight of the layered silicate material.
The composition may further include the use of metal oxides or metal salts that further improve the flame retardant efficiency. Suitable metals, for example, include aluminum, titanium, chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium and tin. Oxides or salts of zinc or manganese, including organic and inorganic salts, are preferred, with zinc borate being most preferred.
The matrix or host polymers that are utilized in accordance with the present invention include thermoplastics and thermosets. Thermosets include suitable polyesters, polyurethanes and epoxies. Thermoplastic matrix polymers include vinyl polymers, such as styrene, styrene copolymers and polyolefins, as well as thermoplastic polyesters and polyurethanes. Polyolefins are made from the polymerization of one or more monomers chosen from the group of ethene, propene, isobutylene, 1-butene, 4-methyl-1-pentene, or alpha-olefins having 5-18 carbon atoms. The polymers may also contain lesser amounts of units derived from copolymerization with monomers such as vinyl acetate and alkyl (meth)acrylate esters like butyl acrylate.
The matrix polymer composition may include fillers, impact modifiers, processing aids and the like, as further hereinafter described.
A large number of siliceous materials may be optionally employed as filler in addition to the other components of the intumescent compositions without changing the basic and novel intumescent character of the compositions imparted by the above-recited ingredients. Suitable filler materials may include diatomite, perlite, pumice, pyrophillite, silica, and talc. These minerals may consist of an alkali metal oxide or alkaline earth element oxide, and silicon dioxide together with a minor amount of water and other elements. Talc, for example, includes from about 25% to about 35% MgO, 35-60% SiO2 and about 5% H2O.
Other fillers such as calcium carbonate may also be employed, as well as reinforcing agents impact modifiers, pigments and the like, as further discussed below.
Fibrous reinforcing agents are commonly: whiskers; glass; mineral wool; calcium sulfate; potassium titanate; boron; alumina; sodium aluminum; hydroxy carbonate; and so forth.
Suitably extruded polymeric compositions may include coloring agents for aesthetic appeal, preferably titanium dioxide, carbon black, and other opacifying agents. The compositions may comprise minor amounts of other additives such as lubricants and antioxidants. These articles of manufacture may be suitably colored with pigments or dyes. Pigments are defined as small insoluble organic or inorganic particles dispersed in the resin medium to promote opacity or translucency. Usual pigments include carbon black, titanium dioxide, zinc oxide, iron oxides, and mixed metal oxides. Dyes are organic and soluble in the plastic, and may be used alone or in combination with pigments to brighten up pigment based colors. All such colorants may be used in a variety of modes which include dry color, conventional color concentrates, liquid color and precolored resin.
The polymeric composition of this invention may further contain one or more agents to improve the impact strength. So-called core-shell polymers built up from a rubber-like core on which one or more shells have been grafted may be used. The core usually consists substantially of an acrylate rubber or a butadiene rubber. One or more shells have been grafted on the core. Usually these shells are built up for the greater part from a vinylaromatic compound and/or a vinylcyanide and/or an alkyl(meth)acrylate and/or (meth)acrylic acid. The core and/or the shell(s) often comprise multi-functional compounds which may act as a cross-linking agent and/or as a grafting agent. These polymers are usually prepared in several stages.
Olefin-containing copolymers such as olefin acrylates and olefin diene terpolymers can also be used as impact modifiers in the present compositions. An example of an olefin acrylate copolymer impact modifier is ethylene ethylacrylate copolymer available from Union Carbide as DPD-6169. Other higher olefin monomers can be employed as copolymers with alkyl acrylates, for example, propylene and n-butyl acrylate. The olefin diene terpolymers are well known in the art and generally fall into the EPDM (ethylene propylene diene) family of terpolymers. They are commercially available such as, for example, EPSYN 704 from Copolymer Rubber Company. They are more fully described in U.S. Pat. No. 4,559,388, incorporated by reference herein.
Various rubber polymers and copolymers can also be employed as impact modifiers. Examples of such rubbery polymers are polybutadiene, polyisoprene, and various other polymers or copolymers having a rubbery dienic monomer.
Styrene-containing polymers can also be used as impact modifiers. Examples of such polymers are acrylonitrile-butadiene-styrene, styrene-acrylonitrile, acrylonitrile-butadiene-alpha-methylstyrene, styrene-butadiene, styrene butadiene styrene, diethylene butadiene styrene, methacrylate-butadiene-styrene, high rubber graft ABS, and other high impact styrene-containing polymers such as, for example, high impact polystyrene. Other known impact modifiers include various elastomeric materials such as organic silicone rubbers, elastomeric fluorohydrocarbons, elastomeric polyesters, the random block polysiloxane-polycarbonate copolymers, and the like. The preferred organopolysiloxane-polycarbonate block copolymers are the dimethylsiloxane-polycarbonate block copolymers in some embodiments.
The present invention is specifically directed to flame retardant compositions as rated, for example, by the UL-94 standard.
The UL-94 standard for tests for flammability of plastic materials for parts in devices and appliances involve several subtests, but the tests of primary interest are small which rate materials 94V-0, 94V-1 or 94V-2. This is a small scale vertical bum test in which a bar of the material to be tested is suspended vertically above a small flame for 10 seconds. The flame is removed and any continued burning time is measured. As soon as the afterflame extinguishes, the ignition source is applied for a second 10 second period, removed, and any residual afterflame or afterglow time is measured. The test is run on 5 specimens to get aggregate as well as individual results. Each bar is 125 mm longxc3x9713 mm widexc3x97minimum and maximum thickness determined by the end use. Typical thickness are {fraction (1/8xe2x80x3)}, {fraction (1/16)}xe2x80x3 and {fraction (1/32)}xe2x80x3 where it is generally more difficult to obtain the highest rating with thinner bars.
Criteria for meeting the various ratings is shown in the following table.
In the following examples, various compositions have been prepared by melt-formulating the various components recited below using an extruder with a barrel temperature of about 400xc2x0 F. followed by injection molding into UL test plaques in a mold at a temperature of about 120xc2x0 F. The plaques were then rated for flammability as noted above.